I think the ceiling is plaster board. Does this mean it should be replaced? We need access to repair the pipe to get my heating going again, but should the whole section of the ceiling come down or could the stained section be cut away and replaced?

Grateful for any suggestions on what kind of tradeperson person should be employed to fix the ceiling (which has halogon light fittings in - would this require an electrician?).

Would this be something to claim on the building's insurance? Any local recommendations?

You probably need to lift your floorboards to effect the repair - rather than to take down your neighbour's ceiling. A plumber would be perfectly able to do that.

As for your neighbour's flat, you don't say how extensive the damage is. A stain can be painted over. You will probably need to use a stain stopping paint - oil based wood primer is highly effective. A decorator would suffice for that.

Soggy plasterboard, however, would be of no further use to man nor beast and would have to be replaced. You would need a builder. No need for a specialist electrician: fitting halogen lights is a doddle.

part P of the building regulations requires that all work on electricals be done by a certified electrician

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Not true. And replacing damaged light fittings in a hallway certainly does not come under the reporting requirements of Part P.

Even if it were to come under the reporting requirements of Part P you still don't require a 'certified' (whatever one of those is) electrician but wihtout one you would require building regs approval.

Quote:

same as corgi for gas

Not true. Not the same as corgi for gas. You are allowed to do DIY gas repairs without involving building regs.